Scope in a Box, troubleshooting question

[Ellie White]

Hi all,

I hope this email finds you well! I had a quick question for you if you don't mind. I was delighted to recently receive a Scope in a Box kit which I plan to demonstrate at a science camp in Green Bank next week. Huge thanks to SARA for kindly providing this kit and for the great instructions that are included! 

I built my Scope in a Box today and attempted some observations, and am a little puzzled by the data I am getting, and wondered if anyone here might have some advice! 

I installed SDR# as well as the IF Average plugin, then after assembling the electronics pipeline as instructed in the manual, I ran a calibration scan (again, following the instructions in the Scope in a Box manual), and once that was complete, attempted to find the HI line. I have attached a screenshot here, which shows the settings I was using as well as the IF Average plot. After a few minutes of integration, it looks like the HI line still was not showing up. I tried calibrating then observing multiple times with the same outcome. 

Note -- when I ran the Calibration scan with the 50-ohm terminator on the LNA, the plot in the IF Average window did look like a pretty typical bandpass plot. I did not capture an image of that but can do so if that would help! 

I would be super grateful for any advice / suggestions! Thank you for your time and for considering this -- have a great evening! 

Cheers,

Ellie

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Ellie White (she/her), KF8GUB

Marshall University - Graduate Asst., Physics

LSST Solar System Science Collaboration - Member

West Virginia Alliance for STEM and the Arts

Phone: 304-654-9381

[Steve Hallman]

You have the RF Gain set to Zero ... Try turning the RF Gain to Maximum 

Steve

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[Ellie White]

Hi Steve,

Thank you so much for the helpful suggestion! I really appreciate it. I just gave that a try, and looks like for some reason I am still not seeing the HI line, see attached screenshot. Not sure what might be going on? Thanks again!! 

Cheers,

Ellie

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[Steve Hallman]

Can you describe you hardware, or provide a photo so I can see your connections.   

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[Steve Hallman]

Hi Ellie;

Also try NOT doing a background subtraction, for now.  If you do a back ground subtraction at the same spot in the sky as you are trying to "see" hydrogen, the "calibration" will subtract out the hydrogen.

Steve

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[Alex P]

Ellie,

Unless you have separately wired it to a battery, the LNA is Unpowered = turn ON the Bias T

( there is a White LED power indicator on the LNA )

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[b alex pettit jr]

also    

[Ellie White]

Hi Alex and Steve,

Thank you both so much! Here is what I have tried so far:

- Turned on the Bias Tee (previously I had plugged the LNA's power cord to a USB port on my laptop, but didn't have the bias T turned on. Even before turning on the bias T, the LED has been on the whole time -- not sure if that meant the LNA was powered or not). 

- Good reminder about making sure the antenna was plugged into the right port -- I verified that the antenna was plugged into the correct port based on the diagram you sent, Alex! 

- Turned up the RF gain all the way, again.

- Tried to record without doing the background subtraction, but found that the gain would get so high that it would go off the IF Average screen even on max gain setting. However, I was doing my calibration scan with a 50-ohm terminator on the antenna input, so hopefully I would not be subtracting out the HI line. 

On my most recent run, it looks like I did pick up some signals, but I'm thinking they are interference (see attached) -- though perhaps I am wrong about that? I know at this point that the galactic plane is pretty low on the horizon here, and my telescope is rigged to point at a high, fixed elevation. I'm not sure if I should expect to see the HI line even when observing well away from the galactic plane or not, and if so, what integration time would be needed to make a clear detection? 

I have attached some photos of my hardware setup as well (apologies for the low resolution, my phone is old haha). 

Thank you all again so much for your guidance and expertise. I appreciate it so, so much!! 

Cheers,

Ellie

On Sun, Jun 28, 2026 at 7:46 PM 'b alex pettit jr' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:

also    

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[b alex pettit jr]

Ellie,

Something is not operating.

Start with simple tests with just using the SDR# Display...  

1) Disconnect the LNA., touch the coax center pin going to the SDR with a piece of wire or paper clip.

If  the SDR is near the PC, You should see a Lot of RFI spikes. 

2) Connect & power up the LNA via Either a battery Or the BiasT but not both and try touching the LNA Input center pin.

Try again .. 

Alex

[Steve Hallman]

Hi Ellie;

In the photo of your radio telescope, the secondary reflector, which sits on the top of the black dipole feed box is missing.  See image below

Steve 

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[b alex pettit jr]

The reflector is not installed on the dipole .. but that is probably not the main issue

I have never attempted to connect the SDR directly to the LNA :

Normally , all digital components ( and USB cable ) create such large RFI that it overwhelms the LNA ..  

Typically, ~ 25 ft of LMR240  ( KMR240) cable or longer should be used to separate analog & digital components

Alex

[b alex pettit jr]

Let me restate that : Digital components should be distanced from the Antenna, not specifically the LNA,

[Ellie White]

Hi Alex,

Thank you so much for this advice! I tried the steps you described, and when I touched a paper clip to the lead of the SDR (without the Sawbird attached), I found that the gain increased but I did not see any interference spikes. I also notice that the NESDR gets quite hot when in use. Do you think perhaps the dongle has gone bad? 

Again, many thanks for your help on this! Have a nice afternoon! 

Cheers,

Ellie

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[b alex pettit jr]

Hi Ellie,

Lets try this another way ... 

1) connect a few feet of wire to the SDR SMA input center pin 

and see if you can tune in an FM radio station : 88 - 108 MHz

if OK,

2) reconnect the LNA but that a wire instead of the antenna on its input

 retune to 1.42 GHz and see if that can pick up RFI .. ( move the LNA near the PC )

( yes, without a background correction, the IFavg plot ampl increases , but it can be brought back into view with the sliders ..  )

For these tests, use an Intermediate avg of 100 vs 1000 multiplier & set dyn ave to ~  100,000

SDRs can run 'warm' I always mount them to a heat sink.

Alex

[Ellie White]

Hi Alex,

Great suggestions, thank you so much! 

1. I was able to successfully pick up FM stations using my NESDR dongle attached to a length of SMA cable, so that is encouraging! 

2. I then tried connecting the Sawbird and attaching the same length of cable as the input, and although again the gain did increase when I plugged in the Sawbird, I am still not seeing any interference spikes. Turns out I had an older Sawbird from a previous project, plugged it in in place of the one that came with the Scope in a Box, and same result - no interference spikes. In both cases, the power LED was on. Curiouser and curiouser! 

Thank you again SO MUCH for your guidance on this, I am so grateful for all your help!! 

Cheers,

Ellie

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[b alex pettit jr]

move the LNA &  'wire antenna' to within a few feet of your PC.

any RFI spikes ?

On Monday, June 29, 2026 at 12:31:58 PM EDT, Ellie White <elliewh...@gmail.com> wrote:

Hi Alex,

[Ellie White]

I tried holding the SMA cable right next to the laptop (the dongle and sawbird were also right next to the laptop) and unfortunately still no spikes, sad to say! (Never thought I'd see the day where I'd be concerned by a lack of RFI 😭)! Not sure what might be going on there. 

Thanks for your patience!! 

Cheers,

Ellie

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[b alex pettit jr]

Maybe the RFI depends on the PC or monitor.

I tried this with another notebook, and I Also, had No  RFI,

However,  the level shifted from around  -57 dB to  -49 dB  Without/With the wire antenna into the LNA

Anything similar to your results ??

No Antenna  - 57 dB

With Wire Antenna -43 dB

Alex

[b alex pettit jr]

Here's another System Operational Test

There should be a substantial  difference between 10K Cold Sky & 290K Earth blackbody noise

What do you measure ??

[Ellie White]

Hi Alex, 

Thank you so much! I just tried both tests, here are the results: 

with wire antenna: -46 dB

without wire antenna: -53 dB

cold sky: -46 dB

hot earth: -46 dB

As you can see -- the wire antenna vs no wire antenna behaved as it should, but for some reason the sky vs earth measurement shows no difference -- that is interesting! Am I right to guess perhaps the issue is to do with either the dish, the feed arm, or the connection between my SMA cable and the cable attachment from the feedarm? 

Again many thanks!! 

Cheers,

Ellie

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[b alex pettit jr]

MayBe there is a problem with the Dipole Feed.

Have a simple DC ohmmeter ?

There should be near Zero Ohms across the SMA connector of the Antenna ..

(   maybe 0.1 - 0.2  Ohm  )

DID you Install the Dipole Reflector before doing the Earth<>Sky test ?

Alex

[b alex pettit jr]

Another test of the Feed

Point antenna Skyward

Record the background level 

Cover the black box of the Feed with Aluminum Foil

Neatness  not required ..

There 'should'  be a several dB change

Alex

[b alex pettit jr]

I tried this with an unmounted feed in the house on a table next to the PC

Normal :           - 54 dB

Foil Covered  : - 60 dB

Alex

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[Mike Otte]

shouldn't the dipole be open circuit??

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Mike Otte W9YS

[Mike Otte]

sma connector come in two flavors :  regular and reverse polarity.   you haven't mixed them?

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[b alex pettit jr]

Nope : it uses a 1/4WL Stub Balun = center cond connected to shield 

[JERRY TAYLOR]

If I remember correctly both sides of the dipole on my Nooelec WiFi dish were connected to the coax shield which doesn’t seem right to me.  Maybe check the dipole connections?  The feed comes apart easily.

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[b alex pettit jr]

That the LNA can be powered via the SDR  BiasT confirms this is not an issue.

[Jason Burnfield]

Another check would be to do an S11 sweep of the dipole with a VNA and make sure it has an appropriate dip near 1420 MHz and that the SWR is in a decent range at this frequency band.

[Conrad Cardano]

Hello

With my scope-in-a-box, I had to lower the feed arm by 100 mm to get it to fit the shape of the antenna parabola.

Conrad

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[Stephen Arbogast]

Yes,   A  few years  ago , with  my first dish, a  wifi dish from  Amazon,  I  first   verified  all  cables, wires  and connectors, supply voltages  with my  multi meter.  Then  using a Tiny Spectrum  Analyzer  I transmitted  the HL  signal about  10 meters away  from  my  dish and went  through stage by stage,  trouble shooting.   At  the  time  I was  using Windows  xx  with  SDR#   and  the  IF  plugin.     I finally  got  all working  but  had to play with settings  in  SDR#  with  IF  plugin  quite a lot.   

I noticed  your  center freq is  1420 Mhz.   Usually  we use  a  center  freq of  1420.500  Mhz.   As for sampling  rate,  bandwidth  I have  been  corrected by  Wolfgang.  See his  comments in other  thread.

Today   I am using Discovery Dish  with  HL   feed... no problems   but  the  Discovery Dish  is the smallest possible  dish to  capture  HL so my  result s do not  look  as  a impressive  as  others.

I have  just  finished an  18 hour  screen cast on  Ubuntu  26.04    using  SDRAngel that is 131.xx  Gig  so  I can't upload it . It is  very  cool.. includes plots  from SDRAngel  and  Stellerium.

Since then  I have  dumped  Windows so sorry  I can't provide  my settings.

Stephen

[Alex P]

Ellie,

If we can't get this working, a very quick build would be the 3 element portion of my 1m long Circular Patch Feed Yagi.

At least for a demo, it works pretty well.

https://github.com/AP-HLine-3D/HLine3D/blob/main/21cm_Step1_Antenna_YagiSE_EnhancedRel_Fab04.pdf

Alex Pettit